Patent GB-790867-A (GB)
Title: Improvements in and relating to apparatus for controlling the operation of turbine-driven alternators
IPC: H02P23/00
Filed: 1955-07-27
Abstract: 790,867. Fluid-pressure servomotor control systems. THOMPSON PRODUCTS, Inc. July 27, 1955 [July 27, 1954], No. 21759/55. Class 135. Apparatus controlling the operation of a turbine-driven alternator, comprises means for detecting variations both in the torque and speed of rotation of the turbine or alternator shafts resulting from changes in alternator load wherein the means is arranged to control a throttle valve in the turbine inlet so that the turbine output matches the alternator load and the rotational speed of the turbine or alternator shaft remains within a predetermined range at all loads. As shown, an alternator 10, Fig. 1, driven by a compressed air turbine 11 which is one of a series of similar turbine-driven alternators connected in parallel to generate electrical power on an aircraft is connected by planetary gearing (not shown) to a torque arm 15 to provide a reverse torque proportional to the alternator load. The arm 15 engages through a variable position member 37 one end of a lever 35 pivoted at 36 and engaging at its other a piston 21 which with shuttle lift valves 23a, 23b controls the supply and exhaust of pressure air to and from the chamber 28 of a servomotor 29 whose piston 30 is connected to the throttle valve 12 in the air supply line 13 to the turbine. The air supplied to the chamber 28 is tapped from the line 13 upstream of the valve 12 to urge the piston 30 upwardly against the lower pressure tapped from the line 13 downstream of the valve. On e.g. an increase in torque consequent upon an increase in alternator load the lever 35 will rotate clockwise to raise the piston 21 and unseat the valve 23a whence the piston 30 will be urged upwardly to increase the throttle valve opening and thus prevent overloading of the alternator and a reduction in its speed. Conversely on a decrease in torque the valve 23b is unseated to vent the chamber 28 whence the piston 30 reduces the opening of the valve 12. An adjustable loading spring 16 acting on the arm 15 prevents a rapid decrease in the alternator load from completely venting the chamber 28 and fully closing the valve 12. To adjust the position of the member 37 a speed-responsive governor 53 driven by the alternator is connected to a piston servo valve 45 to control the supply and exhaust of compressed air tapped from the line 13 upstream of the valve 12 to a double-acting servomotor 42 the piston of which is connected through its rod 40 and a lever 38 to the member 37. At a predetermined alternator speed the governor weights 55 move to the right against the governor spring 57 whence the member 37 is moved leftwardly by the servomotor 42 which reduces the clockwise moment acting on the lever 35 and allows the piston 21 to unseat the valve 23b to vent the chamber 28 and reduce the throttle valve opening to reduce the alternator speed. To provide a speed droop characteristic the action of the governor spring 57 is modified by connecting the valve 45 to a spring- loaded piston 62 subjected to turbine inlet pressure so that as the inlet pressure increases the member 37 will be adjusted leftwardly at a lower speed than would have otherwise been the case. Turbine inlet pressure is stated to be substantially proportional to alternator load so that the alternator speed is slightly decreased in substantially a constant ratio to the load increase. Before starting the alternator, the member 37 is moved to its extreme right position so that the piston 21 is easily raised and the valve 12 soon opened. To provide identical speed versus load droop characteristics for all the alternators, a trim servo 65 actuated by a servo-generator at a control station 70 is provided and is connected through gears 66 to adjust a stop 68 to act in opposition to the spring 57. A speed sensing unit 71 aids the initial synchronization of the alternators. The control station 70 may also be connected with an automatic safety control for the actuation of a cut-off valve 72 located upstream of the valve 12. This valve is controlled by a solenoid 73 which actuates a pilot valve 74 to control a pneumatic actuator 75. In a modified arrangement, a torque arm 15a, Fig. 2, acts directly on a piston 21a which together with a shuttle lift valve 23a controls a double-acting piston 30a connected to the throttle valve 12a. The speed control in this case is applied to a double-acting piston 82 connected to the piston 30a. Governor weights 92 driven by the alternator are connected to a member 85 slidable in a control valve housing 80. Diaphragms 80a, 80b and a web 80c divide the housing into chambers 93, 94, 97 and a shuttle lift valve 88 controls air flow into the chamber 93 from upstream of the throttle valve and leakage therefrom to atmosphere through a duct 87. The chamber 93 is connected to the space below the piston 82 and through a throttle 96 to the chamber 94, to damp the movements of the member 85. The chamber 97 is connected through a restriction 99 and the valve 23a from upstream of the throttle valve and air admitted to this chamber acts on the diaphragm 80b in opposition to the governor spring to provide speed droop. The trim servo 65 driven by the servogenerator at the control station 70 in this case acts on the end of a lever 100. As in the case of Fig. 1, the apparatus provides speed control of the throttle as well as load control. The load control in this instance being applied directly to the piston 21a. On an increase in alternator speed above a predetermined set speed the member 85 moves rightwardly to open the chamber 93 to atmosphere to allow the pistons 82, 30a to move downwardly to reduce the opening of the throttle valve 12a. Conversely upon a drop below the set speed air is supplied to the chamber 93 to move the pistons 82, 30a upwardly to increase the opening of the throttle valve.